What instrument helps a pilot determine if they are at the correct altitude?

The altimeter is a crucial instrument that helps pilots determine their altitude above a reference point, typically sea level. It functions by measuring atmospheric pressure and converting that pressure into an altitude reading. As the aircraft ascends, the atmospheric pressure decreases, and the altimeter needle moves to indicate a higher altitude. Conversely, as the aircraft descends, the pressure increases, causing the needle to reflect a lower altitude.

Accurate altitude measurement is vital for maintaining safe distances from terrain and other aircraft, especially when flying under instrument flight rules (IFR). The altimeter requires regular calibration to the current setting (either from Air Traffic Control or the local altimeter setting) to ensure it reflects true altitude accurately in relation to the specific atmospheric conditions at that time.

The other instruments have different functions: the vertical speed indicator measures the rate of climb or descent, the airspeed indicator provides information on the speed of the aircraft relative to the air, and the artificial horizon indicates the aircraft's orientation relative to the earth's horizon, which is crucial for maintaining level flight but does not directly indicate altitude. Thus, for determining the correct altitude, the altimeter is the primary instrument used.